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參數(shù)資料
| 型號(hào)： | OPA687U |
| 元件分類： | 運(yùn)算放大器 |
| 英文描述： | Wideband, Ultra-Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER With Power Down |
| 中文描述： | 寬帶，超低噪聲，電壓反饋運(yùn)算放大器打倒電源 |
| 文件頁數(shù)： | 10/16頁 |
| 文件大小： | 172K |
| 代理商： | OPA687U |
10
OPA687
signal. If the source is differential already, it may be con-
nected through blocking capacitors into the gain setting
resistors. To set the compensation capacitors for this circuit
(C
S
and C
F
), consider the 1/2 circuit of Figure 4 where the
50
source is reflected through the 1:2 transformer and then
cut in 1/2 and grounded to give a total impedance to AC
ground (for the circuit on the front page of this data sheet)
equal to the 200
.
Considering only the noise gain (this is the same as the non-
inverting signal gain) for the circuit of Figure 4, the low
frequency noise gain, (NG
1
) will be set by the resistor ratios
while the high frequency noise gain (NG
2
) will be set by the
capacitor ratios. The capacitor values set both the transition
frequencies and the high frequency noise gain. If the high
frequency noise gain, determined by NG
2
= 1 + C
S
/C
F
, is set
to a value greater than the recommended minimum stable
gain for the op amp, and the noise gain pole, set by 1/R
F
C
F
,
is placed correctly, a very well-controlled, second-order low
pass frequency response will result.
To choose the values for both C
S
and C
F
, two parameters and
only three equations need to be solved. The first parameter
is the target high frequency noise gain NG
2
, which should be
greater than the minimum stable gain for the OPA687. Here,
a target NG
2
of 24 will be used. The second parameter is the
desired low frequency signal gain, which also sets the low
frequency noise gain NG
1
. To simplify this discussion, we
will target a maximally flat second-order low pass Butterworth
frequency response (Q = 0.707). The signal gain of –4.25
shown in Figure 4 will set the low frequency noise gain to
NG
1
= 1 + R
F
/R
G
(= 5.25 in this example). Then, using only
these two gains and the GBP for the OPA687 (3600MHz),
the key frequency in the compensation can be determined as:
Z
O
=
GBP
NG
1
2
1–NG
1
NG
2
– 1– 2NG
1
NG
2
C
F
=
1
2π
R
F
Z
O
NG
2
C
S
=
NG
2
–1
(
)
C
F
f
–
3
dB
Z
O
GBP
Physically, this Z
0
(4.1MHz for the values shown above) is
set by 1/(2
π
R
F
(C
F
+ C
S
)) and is the frequency at which the
rising portion of the noise gain would intersect unity gain if
projected back to 0dB gain. The actual zero in the noise gain
occurs at NG
1
Z
0
and the pole in the noise gain occurs at
NG
2
Z
0
. Since GBP is expressed in Hz, multiply Z
0
by 2
π
and use this to get C
F
by solving:
Finally, since C
S
and C
F
set the high frequency noise gain,
determine C
S
by [Using NG
2
= 24]:
The resulting closed-loop bandwidth will be approximately
equal to:
For the values shown in Figure 4, the f
–3dB
will be approxi-
mately 121MHz. This is less than that predicted by simply
dividing the GBP product by NG
1
. The compensation
network controls the bandwidth to a lower value while
providing the full slew rate at the output and an excep-
tional distortion performance due to increased loop gain at
frequencies below NG
1
Z
0
. The capacitor values shown
in Figure 4 are calculated for NG
1
= 5.25 and NG
2
= 24
with no adjustment for parasitics. The full circuit on the
front page of this datasheet shows the capacitors adjusted
for parasitics.
The front page of this data sheet shows the measured 2-tone,
3rd-order distortion for just the amplifier portion of the
circuit.
The upper curve is for a total 2-tone envelope of 4Vp-p,
requiring two tones, each at 2Vp-p across the OPA687
outputs. The lower curve is for a 2Vp-p envelope requiring
each tone to be 1Vp-p. The basic measurement dynamic
range for the two close-in spurious tones is approximately
85dBc. The 4Vp-p test does not show measurable 3rd-order
spurious until 25MHz ,while the 2Vp-p is unmeasurable up
to 40MHz center frequency. Two-tone, 2nd-order
intermodulation distortion was unmeasurable for the circuit
on the front page of this data sheet.
(= 1.90pF)
(= 43.8pF)
(= 121MHz)
FIGURE 4.Broadband Low Inverting Gain External Com-
pensation.
R
F
850
C
44pF
OPA687
+5V
–5V
V
O
V
I
C
1.9pF
R
G
200
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| OPA687 | Wideband, Ultra-Low Noise, Voltage Feedback OPERATIONAL AMPLIFIER With Power Down |
| OPA688U | Unity Gain Stable, Wideband VOLTAGE LIMITING AMPLIFIER |
| OPA688P | ECONOLINE: RB & RA - Dual Output from a Single Input Rail- Power Sharing on Output- Industry Standard Pinout- 1kVDC & 2kVDC Isolation- Custom Solutions Available- UL94V-0 Package Material- Efficiency to 85% |
| OPA688 | Unity Gain Stable, Wideband VOLTAGE LIMITING AMPLIFIER |
| OPA689U | Wideband, High Gain VOLTAGE LIMITING AMPLIFIER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| OPA687U/2K5 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier |
| OPA688 | 制造商:BB 制造商全稱:BB 功能描述:Unity Gain Stable, Wideband VOLTAGE LIMITING AMPLIFIER |
| OPA688M | 制造商:TI 制造商全稱:Texas Instruments 功能描述:UNITY-GAIN-STABLE WIDEBAND VOLTAGE LIMITING AMP LIFIER |
| OPA688MJD | 制造商:TI 制造商全稱:Texas Instruments 功能描述:UNITY-GAIN-STABLE WIDEBAND VOLTAGE LIMITING AMP LIFIER |
| OPA688P | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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